Content-Type header with application/json should be assumed if there is a request body

[RobbyUitbeijerse]

Hello!

It feels very logical to us for a default Content-Type': 'application/json' header to be assumed if there are any requestBodyParams. Reasoning being that currently, in the fetch template, the body is provided through JSON.stringify(), but not all services accept the payload if you don't pass the header. I do realize these can simply be passed through options (either per request/global), but the default seems sensible.

Let me know how you feel about it, happy to provide a PR.

[melloware]

This seems reasonable to me. Please submit a PR

[soartec-lab]

@RobbyUitbeijerse

The fetch client doesn't yet support cases other than application/json, such as multipart/form-data and application/x-www-form-urlencoded so i'll do this by following response.

#1387 (comment)

I plan to add a header to the fetch client options when content-type is specifyed in OpenAPI so, i 'll fix this issue as well 👍